[ci skip] Fix to a, b and c format

guides/source/security.md

@@ -754,7 +754,7 @@ s = sanitize(user_input, tags: tags, attributes: %w(href title))
 
 This allows only the given tags and does a good job, even against all kinds of tricks and malformed tags.
 
-As a second step, _it is good practice to escape all output of the application_, especially when re-displaying user input, which hasn't been input-filtered (as in the search form example earlier on). _Use `escapeHTML()` (or its alias `h()`) method_ to replace the HTML input characters &, ", <, > by their uninterpreted representations in HTML (`&`, `"`, `<` and `>`). However, it can easily happen that the programmer forgets to use it, so _it is recommended to use the SafeErb gem. SafeErb reminds you to escape strings from external sources.
+As a second step, _it is good practice to escape all output of the application_, especially when re-displaying user input, which hasn't been input-filtered (as in the search form example earlier on). _Use `escapeHTML()` (or its alias `h()`) method_ to replace the HTML input characters &, ", < and > by their uninterpreted representations in HTML (`&`, `"`, `<` and `>`). However, it can easily happen that the programmer forgets to use it, so _it is recommended to use the SafeErb gem. SafeErb reminds you to escape strings from external sources.
 
 ##### Obfuscation and Encoding Injection